It was working fine for about two days--and then pulled down this WU that it doesn't know how to deal with.

Click to expand...

Normally deleting the work folder does the trick, but it sounds like it just reassigned another P762x to you. They have had problems lately with WU's being assigned to the wrong clients. Most likely, you will just have to give them time.
You may need to let them know like the following thread: http://foldingforum.org/viewtopic.php?f=18&t=23054

I just noticed that one of my WU's is 20+ hours old, and that's on one of my 560 Ti's. Looking into it further, I discovered that there have been various failures but the WU just keeps restarting. I have not seen that before.

I just noticed that one of my WU's is 20+ hours old, and that's on one of my 560 Ti's. Looking into it further, I discovered that there have been various failures but the WU just keeps restarting. I have not seen that before.

Click to expand...

That is truly weird. Is your nvidia driver up-to-date? Perhaps you need to back off your overclock a bit. I know I had to on those 7623's. One of my cards -the cheap bottom of the line Zotac - got too hot. If you're brave (I'm not) try bumping the voltage a bit. Just my 2 cents.